IRREVERSIBLE BLUNTED RESPIRATORY SENSITIVITY TO HYPOXIA IN HIGH ALTITUDE NATIVES

To further explore the blunted hypoxic drive to ventilation seen in the high altitude natives, the steady-state ventilatory response to inhaled CO(in2) at three to four levels of PaO2 was investigated in the following groups of subjects at altitude and at sea level. At altitude (4540 m, Pb 445 mm Hg): 6 high altitude natives, 8 lowlander residents for 1 2 to 35 yr and 3 lowlander visitors for 2 to 3 weeks; at sea level (Pb 758 mm Hg): 3 highlander residents for 10 months and 2 sea level natives. No difference in CO2 sensitivity between the groups at altitude and at sea level was apparent, although the sea level values were lower as expected. Both the interactive and additive effects of hypoxic and hypercapnic stimuli on ventilation were less in the highlanders, and this blunted response was not reversed by 10 months residence at sea level. The sea level natives maintained their higher respiratory sensitivity to hypoxia than the highlanders at 4540 m regardless of the length of acclimatization during adult life. Thus life-long hypoxemia or genetic factors) may have been responsible for the decreased hypoxic ventilatory response in highlanders. © 1969.